Field of the Invention
The present invention relates to a thermal processing method and thermal processing apparatus of heating a thin-plate fine electronic substrate (hereinafter simply referred to as a “substrate”) such as a semiconductor wafer to which impurities are introduced, by irradiating the substrate with light.
Description of the Background Art
In a process of manufacturing a semiconductor device, impurity introduction is a process necessary for forming a p-n junction in a semiconductor wafer. Currently, a typical impurity introduction is achieved by an ion implantation technique and a subsequent annealing technique. The ion implantation technique is a technology in which impurity elements such as boron (B), arsenic (As), and phosphorus (P) are ionized to collide onto a semiconductor wafer with a high acceleration voltage and physically perform impurity implantation. Implanted impurities are activated through anneal processing. In this process, an annealing time of several seconds or longer allows the implanted impurities to deeply diffuse by heat to have a junction depth much larger than required, potentially causing difficulties in favorable device formation.
For this reason, flash lamp annealing (FLA) has attracted attention recently as an anneal technology of heating a semiconductor wafer in an extremely short time. The flash lamp annealing is a thermal processing technology of rising temperature only at the surface of a semiconductor wafer in which impurities are implanted, in an extremely short time (several milliseconds or less) by irradiating the surface of the semiconductor wafer with flash light using a xenon flash lamp (hereinafter, a simple notation of “flash lamp” means the xenon flash lamp).
The xenon flash lamp has an emission spectral distribution ranging from ultraviolet to near-infrared, and has a wavelength shorter than that of the conventional halogen lamp, which is substantially the same as the fundamental absorption band of a silicon semiconductor wafer. Thus, when the semiconductor wafer is irradiated with flash light from the xenon flash lamp, less light is transmitted and thus the temperature of the semiconductor wafer can be rapidly risen. It has been found that the flash light irradiation in an extremely short time less than several milliseconds can selectively rise temperature only at the vicinity of the surface of the semiconductor wafer. Thus, when the xenon flash lamp is used to rise temperature in an extremely short time, only impurity activation can be executed without diffusing impurities deeply.
U.S. Pat. No. 4,649,261 and US2003/0183612 each disclose a thermal processing apparatus employing such a xenon flash lamp, which performs desired thermal processing through a combination of a pulsed emission lamp such as a flash lamp provided on a front surface side of a semiconductor wafer, a continuously lighting lamp such as a halogen lamp provided on a back surface side thereof. In the thermal processing apparatus disclosed in U.S. Pat. No. 4,649,261 and US2003/0183612, the semiconductor wafer is preheated to a certain temperature by, for example, a halogen lamp and thereafter risen to a desired processing temperature through pulse heating by the flash lamp.
Typically, processing, such as thermal processing, of a semiconductor wafer is performed in units of lots (a set of semiconductor wafers to be provided with processing of identical contents under identical conditions). In substrate processing apparatus, of which a semiconductor wafer processing is performed one by one continuously and sequentially on a plurality of semiconductor wafers included in a lot. In a flash lamp anneal apparatus, a plurality of semiconductor wafers included in a lot are transferred into a chamber one by one and are sequentially subject to the thermal processing.
When a flash lamp anneal apparatus that is not operational starts processing of a lot, the first semiconductor wafer of the lot is transferred into a chamber substantially at room temperature and then subject to the heating processing. At the heating processing, the semiconductor wafer supported by a susceptor in the chamber is preheated to a predetermined temperature and then risen to a processing temperature by flash heating. As a result, thermal conduction occurs from the semiconductor wafer the temperature of which has risen to the susceptor and the like in the chamber, and the temperatures of the susceptor and the like rise accordingly. Such an increase in the temperatures of the susceptor and the like due to the heating processing of the semiconductor wafer continues for few semiconductor wafers following the first semiconductor wafer. Eventually when the heating processing is performed on approximately 10 semiconductor wafers, the temperature of the susceptor reaches a stable temperature. In other words, the first semiconductor wafer of the lot is processed being supported by the susceptor at room temperature, whereas the tenth or later semiconductor wafer is processed being supported by the susceptor the temperature of which has risen to the stable temperature.
This causes such a problem that a temperature history is ununiform among a plurality of semiconductor wafers included in the lot. In particular, since several semiconductor wafers following the first semiconductor wafer of the lot are processed being supported by the susceptor at relatively low temperatures, a temperature reached on the surface at the flash light irradiation potentially does not reach the processing temperature. When a semiconductor wafer supported by the susceptor at low temperature is irradiated with flash light, wafer warpage occurs in some cases because of a temperature difference between the susceptor and the semiconductor wafer, and as a result, the semiconductor wafer is potentially damaged.
For these reasons, in the conventional technology, before processing of a lot is started, a dummy wafer that is not a processing target is transferred into the chamber to be supported by the susceptor and is subject to the flash heating processing under condition identical to that of the lot to be processed, so as to rise the temperatures of the susceptor and the like in the chamber in advance (dummy running). The flash heating processing is performed on about 10 dummy wafers, so that, for example, the susceptor reaches a stable temperature, and thereafter, processing of the first semiconductor wafer of the lot to be processed is started. In this manner, a uniform temperature history can be achieved for a plurality of semiconductor wafers included in the lot, and additionally, wafer warpage due to a temperature difference between the susceptor and a semiconductor wafer can be prevented.
However, in such dummy running, a dummy wafer that is not a processing target is consumed, and it takes a considerable time to perform the flash heating processing on about 10 dummy wafers, preventing efficient operation of the flash lamp anneal apparatus.